Recently, a variety of packet communication systems that mainly comply with IP (Internet Protocol) have been developed even in the field of mobile communications as the demand for the Internet communications grows. Particularly, a speed-enhancement and band-broadening technology that has not been provided in the past will be achieved in IMT (International Mobile Telecommunication)-2000, which is placed as a third generation mobile communication system, and packet communications that mainly comply with IP in the field of mobile communications will be widely used.
For example, republished PC application publication No. WO96/21328 (packet transfer method and mobile communication system), Japanese patent application publication (TOKKAIHEI) No. 8-186605 (mobile packet communication method), and so on disclose prior art techniques concerning such a packet transmission system.
FIG. 17 is a block diagram showing the structure of a prior art packet network as disclosed in republished PCT application publication No. WO96/21328. In the figure, reference numeral 8 denotes a mobile terminal, reference numeral 21 denotes a database, reference numerals 22b and 22c denote packet data exchange apparatuses, reference numerals 23a to 23c denote signal processing circuits, reference numeral 24 denotes a subscriber information memory, reference numeral 25 denotes a subscriber information cache memory, and reference numeral 26 denotes a memory for storing information on subscribers which are currently located in a given servicing area.
Next, a description will be made as to an operation of the prior art packet network.
FIG. 18 is a sequence diagram for explaining control in the packet network constructed as shown in the above figure. When an incoming packet arrives at the packet data exchange apparatus 22b (2001), the packet data exchange apparatus 22b determines whether or not subscriber information is cashed. When no cached information exists, the packet data exchange apparatus 22b reads the subscriber information from the database 21 (2004 to 2008) and stores it in the subscriber information cache memory 25 (2009 to 2011). In contrast, when the subscriber information is cached, the packet data exchange apparatus 22b acquires the subscriber information from the subscriber information cache memory 25 (2018 to 2020).
The packet data exchange apparatus 22b then determines if it transfers the incoming packet to which packet data exchange apparatus from the acquired subscriber information (2012 to 2021), and transfers the incoming packet to the other packet data exchange apparatus 22c that manages a servicing area in which the mobile terminal 8 is currently located (2013 or 2022). The other packet data exchange apparatus 22c at which the incoming packet arrives searches for a radio channel number for the mobile terminal 8, which corresponds to the incoming packet (2014 to 2016), and performs transfer of the incoming packet from the packet data exchange apparatus 22c that manages a servicing area in which the mobile terminal 8 is currently located to the mobile terminal 8 by way of the searched radio channel. Packets to be sent to the mobile terminal 8 are thus transferred one by one through the sequential processes mentioned above.
FIG. 19 is a block diagram showing the structure of a prior art mobile packet communication system as disclosed in Japanese patent application publication (TOKKAIHEI) No. 8-186605. In the figure, reference numeral 27 denotes a home switching center, reference numerals 28a and 28b denote switching centers, reference numeral 29a and 29b denote respective routing areas of the switching centers, reference numeral 30 and 31 denote communication terminals, reference numeral 32 denotes an old route, reference numeral 33 denotes a new route, reference numeral 34 denotes a packet communication control information packet or segment that have not yet reached.
Next, a description will be made as to an operation of the prior art mobile packet communication system.
FIG. 20 is a sequence diagram for explaining the operation of the mobile packet communication system that is so constructed as above. The home switching center 27 divides a data packet “1” (2101, 2102) that is sent from the communication terminal 31 that is a sending source to the other communication terminal 30 into segments, and transmits, by radio, those segments starting from a segment “1-1”, which is generated first, to the communication terminal 30 that is a destination one by one (2104). At this time, the switching center 28a stores undelivered segments that have not yet reached until receiving an acknowledgment signal indicating that the reception of the data packet is complete from the communication terminal 30.
When the communication terminal 30 moves to the routing area 29b of the switching center 28b before receiving the next segment “1-2”, the switching center 28b that is the destination to which the communication terminal 30 moves transmits a location registration request (2106) made by the communication terminal 30 to the home switching center 27 and notifies the home switching center 27 that the communication terminal 30 is currently located in the routing area 29b thereof (2107). After updating the location information on the location of the communication terminal 30 according to this location registration request, the home switching center 27 notifies the switching center 28b that the switching center 28a manages the routing area 29a from which the communication terminal 30 moves and also transmits a location registration response to the switching center 28b (2108).
The switching center 28b makes a request of the switching center 28a that manages the routing area 29a from which the communication terminal 30 moves to transfer packet associated information thereto in response to this notification (2109). In response to the request, the switching center 28a transfers control information on packet communication concerning the communication terminal 30 and segments following the segment “1-2”, which have not yet reached, to the switching center 28b (2110). The switching center 28b transmits by radio those segments that have not yet reached to the communication terminal 30 one by one based on the acquired packet communication control information (2113).
When receiving the next data packet “2” destined for the communication terminal 30 from the communication terminal 31 that is the sending source of the packet (2115) after updating the location information on the location of the communication terminal 30, the home switching center 27 transfers the packet 2 to the switching center 28b that manages the routing area to which the communication terminal 30 moves. When receiving the data packet “2” (2116), the switching center 28b divides the data packet “2” into a plurality of segments and transmits by radio the plurality of segments starting from the first segment “2-1” to the communication terminal 30 one by one.
In the prior art mobile IP packet communication system constructed as above and disclosed in republished PCT application publication No. WO96/21328, the packet exchange apparatus 22b stores the information on a routing area in which a destination mobile terminal 8 is currently located, which is obtained when the mobile terminal 8 performs the location registration, in either the database 21 disposed outside the packet exchange apparatus 22b, for storing the location information on the location of the mobile terminal 8, or the subscriber information cache memory 25 within the packet exchange apparatus 22b, reads out the location information on the location of the mobile terminal 8, which the packet exchange apparatus 22b has stored, when transferring packets destined for the mobile terminal 8, and routes the incoming packets to the packet exchange apparatus 22c that manages the routing area in which the destination mobile terminal 8 is currently located based on the location information, and the packet data exchange apparatus 22c transfers the incoming packets to the mobile terminal 8 by way of a searched radio channel. Therefore a problem with the prior art mobile IP packet communication system is that even packet communications between two mobile terminals 8 should be carried out by way of a packet exchange apparatus having visitor area information on the destination mobile terminal 8 and packets cannot be routed directly between two corresponding packet exchange apparatuses that manage routing areas in which the two mobile terminals are currently located, respectively.
In the other prior art mobile IP packet communication system constructed as mentioned and disclosed in Japanese patent application publication (TOKKAIHEI) No. 8-186605, transfer of undelivered packets each including both control information, which is necessary to continue packet communications for the communication terminal 30 that has moved between the switching center 28a from which the communication terminal 30 has moved and the switching center 28b to which the communication terminal 30 has moved, and segments into which each packet is divided is carried out, and they are also transferred from the home switching center 27 to the switching center 28b that manages a routing area in which the communication terminal 30 is currently located by way of a new communication path (i.e., the new route 33) which is established after the communication terminal 30 moves, as in the case where an old communication path (i.e., the old route 32) was established before the communication terminal 30 moves. Therefore, a problem with the other prior art mobile IP packet communication system is that even when a communication terminal that is carrying out packet communications with another communication terminal moves, packets cannot be routed directly between two corresponding packet exchange apparatuses that manage routing areas in which the two communication terminals are currently located, respectively.
Besides the above-mentioned references, there are some references concerning such a prior art mobile IP packet communication system. For example, Japanese patent application publications No. 2000-217157, No. 2000-92562, No. 2000-183873, and No. 11-266278 disclose such a prior art mobile IP packet communication system. Japanese patent application publication No. 2000-217157 relates to a mobile communication multicast packet transmission system that can improve the system efficiency when applying a multicast communication in an IP packet network to mobile communications. Japanese patent application publication No. 2000-92562 relates to a router apparatus that detects movements of a mobile terminal at a high speed. Japanese patent application publication No. 2000-183873 relates to local control through multicasting and global control through unicasting for a data transmission system having a resending control function and a flow control function. Japanese patent application publication No. 11-266278 relates to switching that uses updating of routing information and a virtual connection.
However, neither of these prior art references discloses a technology of encapsulating packets to be transferred with a multicast address and routing the packets directly between source and destination subscriber packet exchange apparatuses, thereby optimizing a routing path between them and reducing the packet transmission delay that occurs between the source and destination mobile terminals.
The present invention is proposed to solve the above-mentioned problems, and it is therefore an object of the present invention to provide a mobile IP packet communication system that can reduce the transfer delay by optimizing a routing path in mobile communications between mobile terminals, and therefore can efficiently carry out packet transfer.